# How did scientists define mass and force back in the days?

• christian0710
In summary, someone probably just used the distance formula m1*d1=m2*d2 and found an object and said "I will assign this object a mass of 1kg" and then used other objects to solve for their mass. So mass is a relationship between 2 mases and their distances from a center point on a balance according to Gravitational mass method.
christian0710
Hi, I'm amazed by all the tools we have in science to measure things indirectly fx measure weight(force) by measuring mass and downward acceleration of an object.

But there seems to be some hidden secrets: How do you invent a concept like mass and force and measure them in the first place? We know that you need force and acceleration to measure mass, but to make equipement like a Newton meter to measure force, you need a known mass to calibrate it to measure force accurately. which invention came first, and how could you define the size of one of them without knowing the other?

I think Mr. Anderson just explained it here: Someone probably just used the distance formula m1*d1=m2*d2 and found an object and said "I will assign this object a mass of 1kg" and then used other objects to solve for their mass. So mass is a relationship between 2 mases and their distances from a center point on a balance according to Gravitational mass method. This way of determining mass must have come before defining intertial mass, because you need mass to calibrate a tool that can measure force.

christian0710 said:
Hi, I'm amazed by all the tools we have in science to measure things indirectly fx measure weight(force) by measuring mass and downward acceleration of an object.

But there seems to be some hidden secrets: How do you invent a concept like mass and force and measure them in the first place? We know that you need force and acceleration to measure mass, but to make equipement like a Newton meter to measure force, you need a known mass to calibrate it to measure force accurately. which invention came first, and how could you define the size of one of them without knowing the other?
You seem to be treating things like Newtons and kilograms as some sort of absolute units. They are not. All measurement units are established by some sort of convention, where a group of people get together and say, a meter is this long, or a kilogram is this much of a substance.

http://en.wikipedia.org/wiki/History_of_the_metric_system

http://en.wikipedia.org/wiki/International_System_of_Units

Because units are based on a convention, the convention can be altered over time, and the definition of various units can subtly change. For instance, a meter is no longer the length of a certain metal rod kept in a vault in Paris, but is now defined as so many wavelengths of the orange-red emission line of Krypton-86.

http://en.wikipedia.org/wiki/Metre

vanhees71 and christian0710
The kilogram is the last unit that still relies on an object (a cylinder in Paris that has a mass of exactly 1 kilogram by definition). Multiple groups try to replace this by a more reliable definition in terms of fundamental physical constants, that would allow to gauge scales without this object in Paris.
Historically, most units were defined based on objects - like a stick that was one meter long by definition, and so on.

SteamKing said:
You seem to be treating things like Newtons and kilograms as some sort of absolute units. They are not. All measurement units are established by some sort of convention, where a group of people get together and say, a meter is this long, or a kilogram is this much of a substance.

http://en.wikipedia.org/wiki/History_of_the_metric_system

http://en.wikipedia.org/wiki/International_System_of_Units

Because units are based on a convention, the convention can be altered over time, and the definition of various units can subtly change. For instance, a meter is no longer the length of a certain metal rod kept in a vault in Paris, but is now defined as so many wavelengths of the orange-red emission line of Krypton-86.

http://en.wikipedia.org/wiki/Metre

I am aware that every unit we made up is "made up" and often relies on other made up units to measuer it indirectly. but I'm interested in the ways people would measure these things back in the days, also how the gravitational constant, electrical constants etc. was measured back then, and then how our modern equipement measures theese things today, but i don't really know if there is any book that goes into detail about that? I'm very interested in the cronological order, so how the first units were made up, then how they were used to derive the next unit (fx the Gravitational constant must have relied on other units and methods to calculate them in order to derive the gravitational constant). I just don't know where to find this information.

I was wondering if what I'm searching for has a name? i stried searching on amazon for "History of SI units" or "development os measurement techniques" but i only find charts.

Last edited:
christian0710 said:
I am aware that every unit we made up is "made up" and often relies on other made up units to measuer it indirectly. but I'm interested in the ways people would measure these things back in the days, also how the gravitational constant, electrical constants etc. was measured back then, and then how our modern equipement measures theese things today, but i don't really know if there is any book that goes into detail about that? I'm very interested in the cronological order, so how the first units were made up, then how they were used to derive the next unit (fx the Gravitational constant must have relied on other units and methods to calculate them in order to derive the gravitational constant). I just don't know where to find this information.

I was wondering if what I'm searching for has a name? i stried searching on amazon for "History of SI units" or "development os measurement techniques" but i only find charts.
Searching on Amazon is not the best way to find out details about a scientific subject. After all, Amazon is a merchant retailer of books, electronics, appliances, etc.

If you want to know how various constants were first measured, stick to web search engines, if you don't have access to anything better.

You must realize that things like the gravitational constant and the various electrical constants couldn't be measured until after people had developed a notion of what gravity is, or what electricity is.

For instance, if you do a web search on "gravitational constant", you will not only find an accurate value of this in modern units, but also articles which deal with its history and how it is measured:

http://en.wikipedia.org/wiki/Gravitational_constant

Similar results can be obtained for other physical constants. To a great extent, it depends on where you look and how long you are willing to look to find this information.

Amazon would be a handy resource if you were looking for a book on the history of science, or the history of physics, for example, which reading would give you a broad introduction to such topics as have been discussed in this thread.

christian0710
mfb said:
The kilogram is the last unit that still relies on an object (a cylinder in Paris that has a mass of exactly 1 kilogram by definition). Multiple groups try to replace this by a more reliable definition in terms of fundamental physical constants, that would allow to gauge scales without this object in Paris.
Which is kind of funny, because originally it was defined just as the mass of one litre of water at a specified temperature.

christian0710 said:
How do you invent a concept like mass and force

In classical mechanics the concept of mass and force have been invented with Newton's definition 2 (classical momentum), lex 2, lex 3 and isotropy.

christian0710 said:
and measure them in the first place?

As already explained, by comparison with a reference. This reference can simply be based on a definition (e.g. 1 l of water at maximum density has a mass of 1 kg) or it can be derived from other references (e.g. 1 N is the force needed to accelerate 1 kg with 1 m/s²).

christian0710 said:
We know that you need force and acceleration to measure mass

To measure mass you need to keep force and acceleration equal for the unknown mass and the reference mass. But you don't need to measure them.

christian0710

## 1. How did scientists in the past define mass?

In the past, scientists defined mass as the measure of an object's resistance to acceleration when a force is applied to it. This was based on the concept of inertia, which states that objects will remain at rest or in motion unless acted upon by an external force.

## 2. What were some of the early methods used to determine mass?

Early methods used to determine mass included simple balance scales and other mechanical devices. However, these methods were limited in their accuracy and precision.

## 3. How did scientists define force in the past?

In the past, force was defined as a push or pull on an object that can cause it to change its velocity or accelerate. This concept was based on Newton's Second Law of Motion, which states that force is equal to mass times acceleration.

## 4. What were some of the early experiments that helped define mass and force?

One of the most famous experiments that helped define mass and force was conducted by Sir Isaac Newton, who used a pendulum to demonstrate the relationship between mass and gravity. Other experiments involved studying the motion of objects and measuring the forces acting upon them.

## 5. How has our understanding of mass and force evolved over time?

Over time, our understanding of mass and force has evolved through the development of new theories, such as Einstein's Theory of Relativity, and the use of more advanced technologies, such as particle accelerators. We now have a more complex and nuanced understanding of these concepts, but they still remain fundamental to our understanding of the physical world.

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